The word hairesis is where we get our word heresy. Initially it simply meant faction or sect, but over time it became closely identified with that which helps sects to form — a distinctive false doctrine or teaching, which the sectarians use to distinguish themselves.
The faction or “sect” of the Saducees (Acts 5:17) is referred to once. There was a faction of the Pharisees who had believed in Christ (Acts 15:5), who also were promoting the false notion that Gentiles had to become Jews in order to become Christians. St. Paul identifies himself has one who had been a member of the Pharisaical faction or sect of the Jews (Acts 26:5).
With the idea that turnabout is fair play, the Christian faith was identified as just such a sect by the orator Tertullus (Acts 24:5) when he made his presentation before Felix. In Acts 24:14, when Paul is responding to Tertullus, he says this — “But this I confess unto thee, that after they way which they call heresy, so worship I the God of my fathers . . .” (Acts 24:14). The Jewish leaders who met with Paul at the very end of the book of Acts had also heard the Christian faith spoken against, and they called it a “sect” (Acts 28:22).
When Paul writes the Corinthians, he laments the divisions among them, but then he goes on: “For there must be heresies among you, that they which are approved may be made manifest among you” (1 Cor. 11:19). It is not clear here is the problem is simply fractiousness, or fractiousness coupled with error. In Galatians 5:20, he lists heresies as one of the works of the flesh, right alongside adultery and drunkenness. In such a context, it is likely that he is now including the idea of false doctrine, leprosy of the heart and mind.
In 2 Peter. 2:1, we have the clear element of falsehood included in a condemnation of this particular vice. “But there were false prophets also among the people, even as there shall be false teachers among you, who privily shall bring in damnable heresies . . .” False prophets and false teachers are clearly not orthodox but divisive. They are divisive and heretical.
The history of the Church has shown us more than one example of this sin without the doctrinal error, this sin as it lines up with the early scriptural descriptions of it. The Donatists would be one example — rigorists who became sectarian in attitude. This is a sin, but it is not as grievous as the latter manifestion. The term heresy generally has taken on the meaning that Peter gives to it. This is the idea that a group distinctive in practice should also be distinctive in theology, and in order to be distinctive in theology it is necessary to depart from the faith once delivered to the saints. So this means that it is not just a mistake to believe that Jesus is not divine, it is also sin and disobedience. It is a work of the flesh.